Just because you aren't disabled doesn't mean you can't get a disabled placard. The parent of a disabled child or the caretaker of a disabled senior can get a tag as long as they are only using it while they are with the disabled person.

Ummm, no, you don't subtract those people. Those people have handicapped passes, they are for use for when they are passengers. Disabled children also have passes too.

At least in my state.

Source: personal experience knowing at least 5 non-motorist (and personally driving them) and 3 children with disabled platecards. My grandma (never knew how to drive) kept hers in my mom's car since my mom was the one driving her 95% of the time. It actually didn't make any sense for her to have one though because she was always pushed in a wheelchair by a non-disabled person.

And zoning laws are purely local as are demographics. So the extremely wealthy burb next door with the reputation of being full of old people might actually need 20% handicapped parking especially if the strip mall has a pharmacy or outpatient clinic. Where I live, not so much, but if a small flash mob of handicapped people descended upon my favorite independent grocery store it ALWAYS has about 30 handicapped spots empty and available. I swear most of those spots have never been parked in. No "leakage strip" that normal parking spots accumulate.

A handicapped flash mob would honestly be kind of cool.